docs: def assert_between(lower_bound, upper_bound, expr, msg_fmt="{msg}"):
      """Fail if an expression is not between certain bounds (inclusive).
  
      >>> assert_between(5, 15, 5)
      >>> assert_between(5, 15, 15)
      >>> assert_between(5, 15, 4.9)
      Traceback (most recent call last):
          ...
      AssertionError: 4.9 is not between 5 and 15
  
      The following msg_fmt arguments are supported:
      * msg - the default error message
      * lower - lower bound
      * upper - upper bound
      * expr - tested expression
      """
  
      if not lower_bound <= expr <= upper_bound:
          msg = "{!r} is not between {} and {}".format(
              expr, lower_bound, upper_bound
          )
          fail(
              msg_fmt.format(
                  msg=msg, lower=lower_bound, upper=upper_bound, expr=expr
              )
          )